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https://issues.apache.org/jira/browse/IMPALA-7559?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16612104#comment-16612104
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Csaba Ringhofer edited comment on IMPALA-7559 at 9/12/18 1:05 PM:
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Yet another update on this: the issue only occurs if all values in the row
group are equal. The reason is that normally parquet-mr does not write
timestamp statistics for int96 timestamps, because it considers the ordering
undefined. The case when min==max is an exception, because ordering doesn't
matter in this case. This logic is at
https://github.com/apache/parquet-mr/blob/b4198be200e7e2df82bc9a18d54c8cd16aa156ac/parquet-hadoop/src/main/java/org/apache/parquet/format/converter/ParquetMetadataConverter.java#L571.
Currently Impala only does utc->local conversion if the Parquet file was
written by parquet-mr (and convert_legacy_hive_parquet_utc_timestamps is true),
so the issue only occurs in this specific case.
Parquet-mr writes statistics that are actually used by Impala only since
PARQUET-1025, so the issue occurs only with relatively new Parquet-mr and any
Impala that uses Parquet stats.
was (Author: csringhofer):
Yet another update on this: the issue only occurs if all values in the row
group are equal. The reason is that normally parquet-mr does not write
timestamp statistics for int96 timestamps, because it considers the ordering
undefined. The case when min==max is an exception, because ordering doesn't
matter in this case. This logic is at
https://github.com/apache/parquet-mr/blob/b4198be200e7e2df82bc9a18d54c8cd16aa156ac/parquet-hadoop/src/main/java/org/apache/parquet/format/converter/ParquetMetadataConverter.java#L571.
Currently Impala only does utc->local conversion if the Parquet file was
written by parquet-mr (and convert_legacy_hive_parquet_utc_timestamps is true),
so the issue only occurs in this specific case.
Parquet-mr writes statistics that actually used by Impala only since
PARQUET-1025, so the issue occurs only with relatively new Parquet-mr and any
Impala that uses Parquet stats.
> Parquet stat filtering ignores convert_legacy_hive_parquet_utc_timestamps
> -------------------------------------------------------------------------
>
> Key: IMPALA-7559
> URL: https://issues.apache.org/jira/browse/IMPALA-7559
> Project: IMPALA
> Issue Type: Bug
> Components: Backend
> Reporter: Csaba Ringhofer
> Priority: Blocker
> Labels: correctness, parquet, wrongresults
>
> UPDATE: the issue turned out to be different than I first thought, see my
> last comment. I will update the description with more details later.
> If the min/max value of a timestamp column chunk is during the hour of the
> Summer->Winter dst change (UTC+2 -> UTC+1 in CET) then stat filtering can
> drop row groups that contain rows that would be "ok" for the predicate
> otherwise.
> To reproduce (on current master branch):
> {code}
> 1. it is assumed that the timezone is CET and that flag
> convert_legacy_hive_parquet_utc_timestamps is enabled
> ( export TZ=CET; bin/start-impala-cluster.py
> --impalad_args="-convert_legacy_hive_parquet_utc_timestamps=true" )
> 2. create a table in hive and fill data in 3 inserts to create 3 files:
> create table t (i int, d timestamp) stored as parquet;
> insert into t values (1, "2017-10-29 02:30:00"), (2, "2018-10-28 02:30:00");
> insert into t values (3, "2018-10-28 02:30:00");
> insert into t values (4, "2017-10-29 02:30:00")
> 3. Query from Impala
> set num_nodes=1;
> select * from t; -- returns all 4 values (same as Hive)
> select * from t where d = "2017-10-29 02:30:00"; -- returns 1 in Impala (Hive
> returns 1,4)
> select * from t where d = "2018-10-28 02:30:00"; -- returns 2 in Impala (Hive
> returns 2,3)
> profile; -- NumStatsFilteredRowGroups: 2 (only one row group should have been
> stat filtered)
> select * from t where d = "2018-10-28 02:30:00" or i = 5; -- returns 2 and 3
> in Impala (same as Hive), because the "or" part disabled stat filtering
> {code}
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